Question

---How long have you been learning Japanese? 

---I’ve been learning it ____________.

1. A.
   when I was 10 years old
2. B.
   since 10 years ago
3. C.
   for 10 years old
4. D.
   in 10 years

Answer 1

B
现在完成时，能够和since +一段时间 ago或for+一段时间连用，故选B